so 
MELANIANA 3 Genera. 
Margins of the aperture of the shell disunited , the right always sharp. 
Melania. — Shell turreted: aperture entire, oval or oblong, effuse at the base; columella 
smooth, incurved. Operculum horny. 
Plate XV. Fig. 13. M. amarula. (Helix amarula. — Linn.) [Mrs. Mawe’s Cabinet.] 
Melanopsis. — Shell turreted : aperture entire, oval-oblong. Columella callous at the 
upper part; truncated at the base, separated from the right margin by a sinus. 
An operculum, 
Plate XV. Fig. 14. M. laevigata. 
Pirena.— Shell turreted : aperture longitudinal, right lip sharp, having a sinus at the 
base, and another at the summit. Base of the columella curved towards the right 
margin: operculum horny. 
Plate XV. Fig. 15. P. terebralis. (Strombus ater. — Linn.) 
PERISTOMIANA 3 Genera, 
Shell operculated, conoidal or subdiscoidal, the margins of the aperture united. 
Valvata. — Shell discoidal or conoidal, the whorls cylindrical, spiral cavity complete, not 
modified by the penultimate whorl; aperture round, the margins united, sharp. 
An orbicular operculum. 
Plate XV. Fig. 16. V. piscinalis. 
Paludina. — Shell conoidal, the whorls rounded or convex, spiral cavity modified by the 
last whorl: aperture rounded-oval, oblong, angular at the summit; the two mar- 
gins united, acute, never reflected outwards. Operculum orbicular and horny. 
Plate XV. Fig. 17- P. vivipara. (Helix vivipara. — Linn.) 
Ampullarja. — Shell globular, ventricose, umbilicated at the base, without any callosity 
on the left lip : aperture entire, oblong, margins united, the right not reflected. 
An operculum. 
Plate XV. Fig 18. A. Guyanensis. 
NERITACEA — 4 Genera. 
Shell fluviatile, or marine , semi-globular or flattened- oval, without columella, the left margin of the 
aperture resembling a half partition. 
(1) Fresh-water shells. 
Navicella. — Shell elliptical or oblong, convex above, summit straight, depressed to the 
margin, concave beneath; the left lip flattened, sharp, narrow, without teeth, 
transverse. A solid flat operculum, having an acute and lateral tooth. 
Plate XV. Fig. 19, 19 (a). N. elliptica. (Nerita porcellana. — Chem.) 
Neritina. — Shell thin, semi-globular or oval, flattened beneath, not umbilicated: aper- 
ture semi-circular, the left margin flattened, sharp ; no teeth or crenulations on the 
surface of the right margin. Operculum furnished with a lateral tooth. 
Plate XV. Fig. 20, 20 (a). N. dubia. (Nerita dubia. — Chem.) 
